Lead-acid batteries conventionally include a multiplicity of cells connected together in series. Each cell consists of a stack of alternating electrodes, namely cathodes and anodes. Often there is a layer of insulation or separator between the electrodes. The separators are saturated, the cells are flooded, or provide in some other manner with an electrolyte (generally sulfuric acid).
In the past, the electrodes have been formed primarily of lead castings, stampings, or an expended mesh of lead or lead compound which provides the structural element to support the active material (lead or lead alloy) of the electrode. When charged, the electrodes become positively or negatively charged, where the energy is stored until used in whatever application the battery is put. The battery may also be recharged from time to time.
Lead has been predominately used in such batteries for a long period of time. While lead is not particularly a good conductor of electricity, it is inherently corrosive resistant to the electrolytic acids flooding the battery case. Other, more conductive metals are either too expensive to be used as the electrodes for lead-acid batteries, or else they are quickly corroded during the charging action by the electrolytic acids. Therefore, lead has remained as the predominant material. However, lead is also very heavy, and in applications where weight is a factor, other alternatives have long been sought.
For example, in the aircraft industry, experts have calculated that the fuel cost of flying a commercial airliner is more than $3,000 per year per pound of weight flown. Therefore, as opposed to batteries having lead plates, considerable sums of money could be saved per plane if a lighter weight electrode material could be found.
In previous attempts, one approach has been to plate lead onto other more conductive metals or metal alloys such as aluminum and copper. For example, copper is sixteen times as conductive as lead and weighs only about 70% as much. Aluminum, on the other hand, has a specific gravity of only 20%-25% of lead and has approximately eight times the conductivity of lead. Obviously, from the standpoint of weight and conductivity, copper and aluminum are good candidates to replace lead as the substrate for electrodes. However both materials are very susceptible to corrosion in the presence of sulfuric acid, and cannot be used as the positive or current collecting electrode in a lead acid battery if left unprotected. Either material can be used as the negative electrode, and copper has in the past been typically chosen. Previous attempts to use aluminum or copper as the structural element for the positive electrodes of a lead acid battery have been directed to plating lead coatings onto aluminum or copper substrates. The conventional manner for plating lead is from an aqueous solution. The problem arises that when lead is plated from an aqueous solution, for one reason or another, the coatings are porous, and the sulfuric acid will quickly penetrate the coatings and attack the aluminum or copper. In such instances, the copper and aluminum plates have not survived the charging operation.